1. Field of the Invention
The present invention pertains generally to ice making apparatus using a gravity water flow and recirculation system, and more particularly to an ice maker having improved controls for freeze and harvest cycles.
2. Description of the Prior Art
Ice cube makers employing gridded freeze plates forming lattice-type cube molds and having gravity water flow and ice harvest are well known and in extensive use. Such machines have received wide acceptance and are particularly desirable for commercial installations such as restaurants, bars, motels and various beverage retailers having a high and continuous demand for fresh ice.
A leading example of this type of ice cube maker is made by Manitowoc Company, Inc. and disclosed in its Dedricks et al. U.S. Pat. No. 3,430,452, and control improvements of Manitowoc are disclosed in its Schulze-Berge U.S. Pat. Nos. 4,480,441 and 4,550,572.
Another example of lattice-type cube makers is disclosed in Van Steenburgh U.S. Pat. Nos. 4,341,087 and 4,366,679 assigned to Mile High Equipment Company.
Other patents having ice cube makers of this general type include Kattis U.S. Pat. No. 3,144,755; Johnson U.S. Pat. No. 3,913,349; Nelson U.S. Pat. No. 4,471,624 assigned to King-Seeley Thermos Co.; Josten et al. U.S. Pat. No. 4,733,539 assigned to Schneider Metal Mfg. Co. and Toya U.S. Pat. No. 4,727,729 assigned to Hoshizaki Electric Co. (Japan).
There have been various problems associated with commercial ice making machines, particularly in the production of a substantially consistent and uniform cube size in various types of environmental settings. Cyclical ice makers that initiate a harvest cycle by sensing evaporator refrigerant pressure or temperature have a common problem in determining ice size due to the variation in refrigerating capacity in response to changes in ambient air temperature as well as from poor maintenance, such as failure to keep air-cooled condensers clean. The tendency for the evaporator control is to produce premature or undersized ice cubes when condensing capacity is greatest, such as at low ambient air conditions. The reverse is true when condensing capacity is reduced by reason of high ambient air temperatures or fouled condensers. In this case, ice size becomes unacceptably large, and in some cases the ice may not harvest at all if the control set point cannot be reached due to this lowered refrigerating capacity. Thus, where an ice maker is installed in an outdoor location, such as a motel or service station, and subjected to wide seasonal temperature changes, the cube size can vary appreciably from a thin, undersized cube in the winter to an oversized cube in the summer. Furthermore, the time cycle of making such cubes is directly affected by such ambient changes.
It has been proposed that systems can compensate for this problem by using a combination of evaporator pressure (or temperature) and time in controlling the cyclical defrosting cycle. The evaporator pressure (or temperature) sensing point is raised to trip earlier in the cycle and initiate a fixed time period through a mechanical or electronic timer that starts the harvest cycle. Such a system is, at best, an approximation and still allows a wide variation in ice cube size, with accompanying loss of reliability over the ambient air temperature range and operating conditions to which many ice makers are exposed.